In modern controls for motor vehicles and especially for drive units, controllers are often utilized which actuate an actuator in dependence upon the deviation between a pregiven desired value and an actual value of the operating value to be controlled. This actuation is in the sense of bringing the operating variable close to the desired value. Examples of such controllers are controllers for controlling the idle rpm, for controlling the position of a throttle flap, for controlling or limiting the road speed, et cetera. These controllers include controller constants, such as proportional constants, integral constants and/or differential constants whose magnitudes are determined in advance with a view toward the desired stability and dynamic of the control operation. It has been shown that a single set of the above-mentioned variables is not sufficient in all areas of application for a satisfactory control over the entire operating range of the controller. This applies especially to the application of actuators having a large nonlinearity.
One example of an actuator having a large nonlinearity is known from U.S. Pat. No. 4,947,815. The throttle flap actuator described therein includes an emergency air position pregiven by springs. That is, the emergency air position is that position which the throttle flap assumes when no power is supplied to the electric motor driving the throttle flap. If this emergency air position is to be passed through, the sign of the drive torque of the actuator motor reverses. This nonlinearity of the actuator element leads to the condition that a compromise for the determination of the parameter set for the controller is achieved only with difficulty. The control performance is therefore not satisfactory in all operating situations.
A PID position controller is disclosed in German patent publication 4,223,253 which is operated with different sets of parameters in order to achieve a different dynamic in various operating modes such as idle control, drive slip control, et cetera. Operation is with fixed parameter sets within individual operating phases so that the above-mentioned problems occur when driving an actuator which is very nonlinear.
U.S. Pat. No. 4,441,471 discloses an example of an idle rpm control wherein the control parameters are pregiven in dependence upon the difference between the desired and actual values.